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Obesity and Breast Cancer Survival: Talking with Anne McTiernan

Today’s issue of Cancer Research Update highlights a new analysis of the research suggesting that obesity links to poorer survival for women diagnosed with breast cancer. The research adds to a complex and evolving field of research on lifestyle and survivorship.

The findings in this paper add to the body of knowledge, but they are not proof that weight loss in overweight or obese women will improve survival, says Anne McTiernan, MD, PhD, one of the authors of the new paper and a Continuous Update Project expert panelist.

Here, Dr. McTiernan — the Director of the Prevention Center at the Fred Hutchinson Cancer Research Center — talks about the study and what it means for breast cancer survivors.

Q: This study is the first to look at BMI pre- and post-diagnosis, and 12 months following diagnosis. Why was it important to look at these three points?

A: While it’s interesting to know what effect BMI before diagnosis has, women want to know what they can do now, for their future. So it’s important to look at the post-diagnosis period.

Many women have intensive treatments that extend for a year after diagnosis (chemo, radiation, several surgeries), so it can be helpful for them to know if their weight during this period is important. But probably the time for most changes will be after intensive therapy, when women want to know what they can do now. Many women will now be offered very long-term treatments with medications to block estrogens like tamoxifen, or to prevent estrogens from being produced like aromatase inhibitors. So the thinking is that breast cancer treatment will be life-long, and lifestyle change could be part of that treatment.

Q: Can you state the key findings of the paper?

A: This study represents the largest, most complete, analysis of all previous studies on body size and risk of dying in women who have been diagnosed with breast cancer. Increased body size is significantly related to survival after a diagnosis of breast cancer, although there is also evidence that women who are underweight may also have increased risk.

The findings are not proof, however, that weight loss in overweight or obese women could be lengthen life. To say that, we would need evidence from a clinical trial, the gold standard for treatment in cancer patients and survivors.

Q: As you know, obesity is protective for premenopausal breast cancer, but this paper found it was not protective against earlier mortality. What can you take away from this?

A: We know from some other research that some things caused by obesity (like excess production of insulin, elevated levels of body-wide inflammation, excess levels of estrogens and testosterone) are associated with poorer survival in breast cancer survivors. This may be because these factors promote growth of breast cancer cells throughout the body. These associations seem to be true for breast cancer in both pre- and post-menopausal women.

Q: Previous research has suggested an obesity paradox; how being overweight – not obese – may offer some health benefits, including longer survival. But this study did not find that.

A: The factors I listed – excess insulin, inflammation, estrogens, testosterone – start to rise with just a little extra weight. That means you don’t have to be obese to have your fat cells produce these factors. So I wasn’t surprised that being overweight increased risk of poorer survival, similar to the obesity effect.

Q: Many women gain weight with treatment; how does that play into the findings?

A: Some chemotherapy regimens can cause a large weight gain. However, women treated with just tamoxifen or aromatase inhibitors don’t necessarily gain weight from their medication.

Most women in the Western world tend to gain weight each year, and I think that’s what we are seeing with breast cancer survivors. Plus many survivors decrease their level of physical activity and increase intake of “comfort” foods. [These foods] tend to be high in fat and sugars, which can increase daily caloric intake.

Q: I know the conclusion state more research is needed… is there anything to say now?

A: For most survivors I would suggest that they try not to gain weight through their treatments, and try to be as physically active as they can tolerate. Increased physical activity has been shown to improve quality of life and fatigue in survivors, which are very important for women going through a cancer diagnosis and treatment, and beyond. Some women find there are some days when they are more energetic during their active treatments, so those might be the days to take a walk or do some other exercise they might enjoy.

And women should follow as healthy a diet as possible, avoiding high-calorie drinks that tend not to be filling (like juices, sodas, sweetened coffees, alcohol), eat more vegetables and fruits, and lower amounts of high-calorie deserts and sweets. There’s no guarantee these eating styles will improve survival, but they might help women keep their weight stable. For the small number of women who are underweight or losing too much weight during treatment, then the advice would be to work with their medical provider to make sure they are taking in the calories they need.

With regard to purposefully losing weight—we really do need randomized clinical trials before we can definitively say what effect that will have on survival.